In the production of a spectacle lens, a blank is generally first of all cast from a suitable plastic and, in a second manufacturing step called the prescription lens manufacture, is brought to the final shape to achieve the prescription values. The prescription lens manufacture involves work to remove material. To minimize the necessary stock of blanks, these blanks are generally made available only in rough gradations as regards diameter and curvature of the front and back surfaces. Therefore, in the prescription lens manufacture, it is generally necessary to remove a considerable amount of material, usually with about 70% by weight of the material of the blank being removed and discarded. Recycling of this material is not possible.
To machine the blank in the prescription lens manufacture, a block piece has to be attached to the blank, via which the blank can be retained for working in a suitable machine tool. To mount the blank on the block piece, a low-melting metal alloy is generally used. Only a small surface area of the blank is generally blocked, since the heavy-metal alloys used are very expensive and, what is more, very elaborate cleaning of the waste water is necessary in order to avoid contamination thereof with heavy metals. During the machining, the protruding lens edges tend to experience undesired oscillations or to yield and fracture. The oscillation can result in a surface having an undesired structure, and the latter cannot be polished out, since oscillation and yielding of the lens edge also occur during the polishing. Moreover, the outer area is pressed downward during the machining and snaps back again after the loading, as a result of which a kind of bead can form on the unmachined back surface.
It has already been proposed (WO 2011/110300 A2), in a conventional mold, to provide a mold shell with an integrated block piece. After the casting, the blank remains adhering with a surface (the front surface or back surface) to this mold shell and, by means of the integrated block piece, can be machined in the prescription lens manufacture (on the opposite surface).
United States patent application publication 2011/0018150 A1 discloses a method for producing a spectacle lens, in which method the as yet unpolymerized resin is introduced into a mold, the front and rear faces of which are flexible and transparent. The document proposes that the as yet uncured resin is shaped, in front of the eye of the future wearer of the spectacles, via the flexible faces, such that a lens with the desired correction values is obtained. It appears doubtful whether such a method is practicable.
United States patent application publication 2009/0179339 discloses a mold and a sealing ring for producing a spectacle lens.